If you are flying in from Sweden, the closest major airport is Helsinki Vantaa Airport. In August, daytime highs in Helsinki are 24°C, while nighttime lows are 13°C. Wrap up your sightseeing on the 22nd (Wed) to allow time to travel back home.

You can drive from Helsinki to Porvoo in an hour. Alternatively, you can take a bus. In August, daily temperatures in Porvoo can reach 23°C, while at night they dip to 13°C. Wrap up your sightseeing by early afternoon on the 25th (Sat) to allow enough time to drive back home.